Does one of the blood tests that I get tell them if I am in the therapeutic levels? Or, if it starts working, that's how they will know? And I guess there is a fine line between toxic levels and therapeutic levels? Is this different than them checking my WBC?

I assume you are talking about your Imuran? Therpeutic levels are determined by the Prometheus metabolites test. It will show if you are in the proper range. The toxic levels are determined by regular blood tests - the liver function test.

Oops, I need to change my sig. Actually I ended up in the hospital on Imuran, then they put me on 6MP, started getting sick so we thought it was the 6MP. Well, it turns out (thankfully) that I was just starting another flare and we had to up the dosage of prednisone until the 6MP kicks in.

I was on 6mp for about 9 months when my daughter gave me a stomach bug. I was in remission at the time and was thrown into a flare. At that time I wasn't able to reach remission again and I continued to flare. It was during that time that the doc did repetitive Prometheus tests to see if I was metabolizing it right. I did have a few before then and I was always on the low end of the proper range. But even after upping the dose, I was still unable to reach the right range and I was just below the toxic level. So it depends on a couple of factors really and when your doc wants to run the Prometheus test. However, frequent regular blood testing is crucial. It checks your WBC as well as your liver enzymes. So the Prometheus, the WBC and the liver enzyme tests are 3 seperate things but the blood can be taken at the same time.